Cooling device for a condenser of a system for a thermodynamic cycle, system for a thermodynamic cycle, arrangement with an internal combustion engine and a system, vehicle, and a method for carrying out a thermodynamic cycle

ABSTRACT

A cooling device for a condenser of a system for a thermodynamic cycle, with a coolant circuit, wherein a conveying device for conveying a coolant through the coolant circuit is provided, and wherein the coolant circuit includes a cold branch downstream from a cooling point for the coolant and a hot branch upstream of the cooling point. The conveying device has a variable output, and/or the coolant circuit has a connecting line between the hot branch and the cold branch. A mixing device is provided, by way of which a variable portion of coolant can be supplied from the hot branch to the cold branch via the connecting line, bypassing the cooling point.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority of DE 10 2014 206 026.5, filedMar. 31, 2014, the priority of this application is hereby claimed andthis application is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The invention pertains to a cooling device for a condenser of a systemfor a thermo-dynamic cycle, to a system for a thermodynamic cycle, to anarrangement consisting of an internal combustion engine and such asystem, to a motor-driven vehicle with a corresponding arrangement, andto a method for carrying out a thermodynamic cycle.

Thermodynamic cycles of the type in question here are known as such. Aworking medium is heated, in particular vaporized, in a vaporizer, andthen expanded in an expansion device, wherein heat of the working mediumtaken up in the vaporizer is converted to mechanical energy. The workingmedium is then cooled, in particular condensed, in a condenser, and sentback to the vaporizer again. The organic Rankine cycle, for example,corresponds essentially to the Clausius-Rankine cycle, except that it isadapted to lower working temperatures. It is therefore especiallyadapted to the use of waste heat of industrial processes, for example,or to that of internal combustion engines. To cool, in particular tocondense, the working medium in the condenser, a cooling device isprovided. This can be configured as an air cooler, for example, whereinthe cooling capacity of the cooling device is set in this case by theautomatic control of a blower. The disadvantage of this is that theblower has a very high energy demand. It is also possible for thecooling device to provide a direct connection between the condenser andan external heat reservoir in the form of tap water, river water, or seawater, for example. In this case, the cooling capacity available for thecondenser is determined, so that the condenser is limited to operationon a certain temperature level and thus at a certain condensationpressure. This necessarily leads to a performance yield lower thanmaximum possible yield at many operating points of a system foroperating thermodynamic cycles. If, furthermore, the temperature of theworking medium at the outlet from the condenser varies with theoperating point of the system as a result of the fixed cooling capacity,it is possible that, at certain operating points and especially in highload ranges of the system, it is impossible to ensure sufficientsupercooling of the working medium below its condensation point in thecondenser, as a result of which there is the danger that cavitationswill occur in the conveying device of the system set up to convey theworking medium through the circuit.

SUMMARY OF THE INVENTION

The invention is based on the goal of creating a cooling device by meansof which the disadvantages cited above can be avoided. The invention isalso based on the goal of creating a corresponding system, anarrangement consisting of an internal combustion engine and a system, amotor-driven vehicle, and a method for operating a thermodynamic cycle,wherein the cited disadvantages do not occur.

The goal is achieved in that a cooling device is set up to cool acondenser of a system for operating a thermodynamic cycle, highlypreferably an organic Rankine cycle, known by the abbreviation “ORC”,wherein the cooling device comprises a coolant circuit. A conveyingdevice for conveying a coolant through the coolant circuit is provided.The coolant circuit comprises a cold branch upstream of a cooling pointfor the coolant and a hot branch downstream from the cooling point.According to a first exemplary embodiment, the cooling device ischaracterized in that the conveying device comprises a variable output.As a result, the cooling capacity of the cooling device can always beadapted to the current operating point of the system for thethermodynamic cycle by variation of the output of the conveying device,so that the temperature level and thus the condensation pressure in thecondenser can always be set precisely. Alternatively, according to asecond exemplary embodiment, it is provided that the coolant circuitcomprises a connecting line between the hot branch and the cold branch,wherein a mixing device is provided, by means of which a variableportion of the coolant can be sent from the hot branch to the coldbranch via the connecting line, thus bypassing the cooling point. As aresult, a temperature level of the coolant upstream of the condenser isadjustable, as a result of which in turn the cooling capacity of thecooling device can be adjusted. This device can therefore always beadapted in this way as well, exactly and precisely, to an operatingpoint of the system.

The cooling point refers to an area of the coolant circuit in which thecoolant is cooled, in particular recooled, wherein the heat taken up bythe coolant in the condenser is carried away here. The cold branch ofthe coolant circuit connects the cooling point to the condenser, so thatcooled coolant can be supplied to it, wherein the hot branch connectsthe condenser to the cooling point, so that coolant heated in thecondenser can be sent to the cooling point for cooling. The coolingdevice is to this extent not configured as an open system with directconnection of the condenser to the environment or to an external heatreservoir, but rather as a recooled primary coolant circuit, which isitself cooled in the area of the cooling point.

In an exemplary embodiment of the cooling device, the conveying deviceis configured as a pump, wherein the output of the pump is variable, inthat it has a variable rotational speed.

A portion of coolant taken from the hot branch and variable in themixing device can be adjusted in particular to achieve a desired ratioof a volume flow rate of the coolant flowing via the connecting line toa volume flow rate flowing via the cooling point. It is obvious thatcold coolant thus arriving in the mixing device from the cooling pointcan be mixed with hot coolant arriving from the condenser and branchedoff upstream of the cooling point, so that ultimately in this way thetemperature of the coolant supplied to the condenser for cooling isadjustable.

In a third exemplary embodiment of the cooling device, both theconveying device comprises a variable output and the coolant circuitcomprises a connecting line between the hot branch and the cold branch,wherein a mixing device is provided, by means of which a variableportion of coolant from the hot branch can be supplied to the coldbranch via the connecting line, thus bypassing the cooling point. Inthis way, there are two degrees of freedom available for automaticallycontrolling the cooling capacity, so that this capacity can be set veryprecisely and independently of the temperature level of the coolingpoint. Thus the condensation pressure in the condenser is preciselyadjustable and adaptable to any operating point of the system which mayoccur. An optimal power yield can therefore be ensured at all operatingpoints, and the cooling of the condenser is not limited by a fixedcooling capacity to a certain temperature level and thus to a certaincondensation pressure. The conveying device, especially when it isconfigured as a variable-speed pump, consumes in particular much lesspower than the blower of an air-cooled condenser. In addition, thecooling capacity of the cooling device proposed here can be set moreprecisely than is possible with air cooling with ambient air by means ofa blower.

An exemplary embodiment of the cooling device is characterized in thatthe conveying device is configured as an automatically controllableconveying device. As a result, the flow rate of the coolant through thecoolant circuit, in particular the volume flow rate of coolant throughthe condenser, can be set especially accurately. It is possible for aconveying line of the conveying device to be automatically controlled toset the volume flow rate through the condenser. It is especiallypreferable for the conveying device to be configured as an automaticallycontrollable pump. The rotational speed of the pump is preferablycontrollable, which represents an especially simple embodiment of anautomatically controllable conveying device.

An exemplary embodiment of the cooling device is characterized in thatthe connecting line branches off from the hot branch upstream of arecooling device, wherein the recooling device is set up to cool thecoolant in the coolant circuit. The connecting line leads to the coldbranch downstream from the recooling device. The cooling point of thecooling device in this exemplary embodiment is realized by the recoolingdevice, wherein preferably the primary cooling circuit realized by thecoolant circuit is connected for heat transfer to a secondary coolantcircuit. Alternatively, it is possible for the recooling device toconnect the coolant circuit to an external heat reservoir by way of athermal connection. The recooling device is preferably configured to useoutside water or air as coolant, in particular tap water, river water,sea water, or ambient air. Especially in the case of marine applicationsof the system, recooling by sea water is preferred. By means of therecooling device, the coolant can be cooled very effectively in the areaof the cooling point, wherein its waste heat can be dissipated to theenvironment easily and at low cost. Because the connecting line branchesoff from the hot branch upstream of the recooling device,as-yet-uncooled coolant heated in the condenser can be sent through theconnecting line. Because the connecting line leads to the cold branchdownstream from the recooling device, it is possible at this point, atwhich preferably the mixing device is also provided, to mix cold coolantarriving from the recooling device especially efficiently with hotcoolant arriving via the connecting line.

Another exemplary embodiment of the cooling device is characterized inthat the connecting line leads to the cold branch upstream of theconveying device. Thus the mixing device is also preferably arrangedupstream of the conveying device, so that it conveys coolant which hasalready been mixed and is thus at the specified temperature reached inthe mixing device. In terms of automatic control technology, this provesto be especially favorable, and it is easier than if the connecting linewere to lead to the cold branch downstream from the conveying device,which would mean that the conveying device was merely conveying coldcoolant.

An exemplary embodiment of the cooling device is characterized in thatthe mixing device is configured as a three-way mixer, wherein the coldbranch leads to a first and a second connector of the three-way mixer,wherein the connecting line leads to a third connector of the three-waymixer. The part of the cold branch arriving from the cooling point leadsto a first connector of the three-way mixer, wherein the path of thecoolant continues from a second connector of the three-way mixer to thecondenser. The connecting line is connected to the third connector ofthe three-way mixer, so that coolant from the first and third connectorsis mixed in the mixing device and sent to the second connector. Thisrepresents an especially simple and low-cost as well as easy-to-controlembodiment of the mixing device. The mixer can comprise a firstfunctional setting, in which the first connector is connected to thesecond connector, wherein the third connector is blocked. In this case,the mixing device allows only cold coolant through, so that, to thisextent, a minimum temperature of the medium is realized. In a secondfunctional setting, the third connector is connected to the secondconnector, wherein the first connector is blocked. In this case, themixing device allows only hot coolant through, so that to this extent amaximum temperature of the medium is realized. Between these two extremepositions, there are preferably various functional settings, especiallypreferably a continuum of functional settings, that can be realized, sothat the temperature of the coolant can be adjusted by the mixing deviceto any or to almost any temperature between the minimum temperature andthe maximum temperature of the medium.

In another embodiment the cooling device is characterized by controlunit, which is set up to produce a presettable absolute or relativetemperature level in a condenser of a system for operating athermodynamic cycle, highly preferably an ORC, by actuating theconveying device and/or by actuating the mixing device. The control unitis set up preferably to produce the desired temperature level byactuation of both the conveying device and the mixing device. By meansof the control unit, it is possible in any case to produce an absoluteor relative temperature level in the condenser in a highly exact andprecise manner, preferably to control it in an open-loop or closed-loopmanner.

An absolute temperature level is understood to mean an absolute,previously determined temperature to be reached for the working mediumin the condenser or directly downstream from the outlet of the workingmedium from the condenser. A relative temperature level is understood tomean a previously determined degree of supercooling of the workingmedium in the condenser or directly downstream from the condenser,therefore a previously determined difference between the working mediumtemperature and the condensation point of the working medium in thecondenser. By effectively adjusting the degree of supercooling, it canbe ensured that the working medium does not cavitate in the workingmedium pump of the system. By way of the adjustment of the absolute orrelative temperature level in the condenser or directly downstream fromthe condenser, furthermore, the power yield of the system can also beoptimized. What is needed for this purpose in particular is the preciseadjustment of the pressure in the condenser, which can be adjusted veryprecisely by variation of the working medium temperature and thereforeby variation of the cooling capacity of the cooling device. Thispressure acts as a backpressure at the expansion device and therefore,together with other operating parameters of the system, plays a primaryrole in determining the power yield of the system. The cooling capacitywhich the cooling device must have to adjust the temperature level to apresettable value varies as a function of the operating point of thesystem, in particular as a function of the heat input into the system,because, depending on the heat input into the vaporizer, a greater orlesser amount of heat must be carried away from the condenser. By meansof the cooling device proposed here, it is to be prevented in particularthat more heat is carried away than is necessary to achieve a previouslydetermined supercooling of the working medium. Otherwise this has anegative effect on the power yield of the system.

The control unit is set up to maintain the preset volume flow rate ofthe coolant via automatic control of the output of the conveying deviceand to maintain the preset coolant temperature at the inlet into thecondenser by actuating or automatically controlling the mixing device.In this way, the cooling capacity of the cooling device can becontrolled very sensitively by the control unit in either open-loop orclosed-loop fashion, especially by combining the variation of the outputof the conveying device with the variation of the temperature setting inthe mixing device.

An exemplary embodiment of the cooling device is characterized in thatthe control unit is set up to optimize the power yield of the system byactuation of the conveying device and/or of the mixing device. In thiscase, the control unit preferably comprises a feedback circuit for atleast one parameter which is a characteristic of the power yield of thesystem, so that the power yield can be optimized directly, i.e.,automatically controlled. As a result, the cooling capacity of thecooling device can always be coordinated optimally with the currentoperating point of the system. It is especially preferable for thecontrol unit to be set up to optimize the power yield of the system byactuating both the conveying device and the mixing device.

The goal is also achieved in that a system for operating a thermodynamiccycle, quite preferably an organic Rankine cycle, is created, which ischaracterized by a cooling device according to one of the previouslydescribed exemplary embodiments. The advantages already described inconjunction with the cooling device are thus realized for the system. Inparticular, the system can be automatically regulated by way of thecooling device to deliver an optimal power yield at all operatingpoints.

The system comprises a working medium circuit, around which a vaporizer,an expansion device, a condenser, and preferably a working medium pumpfor conveying working medium through the circuit are arranged—in thatorder. The cooling device is functionally connected to the condenser sothat the working medium can be cooled in the condenser.

The system also comprises at least one temperature sensor and/or atleast one pressure sensor in the condenser or directly downstream fromthe condenser, i.e., downstream with respect to the direction in whichthe working medium flows through the circuit, this sensor beingfunctionally connected to the control unit for the open-loop orclosed-loop control of the cooling device. By the use of the temperaturesensor and/or the pressure sensor, a thermodynamic state of the workingmedium in the condenser can be acquired, and the cooling capacity of thecooling device can be adjusted on that basis, adjusted in particular inan open-loop or closed-loop manner.

An exemplary embodiment of the system is characterized in that it is setup to use waste heat of an internal combustion engine. For this purposein particular, an ORC is preferably carried out in the system. It ispossible in this case to make use of the waste heat in an exhaust gasstream or in a coolant stream of the internal combustion engine.Alternatively, it is possible that the system could be set up to usewaste heat or heat from some other heat source such as industrial wasteheat and/or to use geothermal heat, preferably also by means of an ORC.

Ethanol is preferably provided as the working medium in the system. Thisis especially well adapted to the operating points in the system whichare reached during the use of waste heat from the exhaust gas of aninternal combustion engine and is also well adapted to an ORC.

The goal is also achieved in by an arrangement that comprises aninternal combustion engine and a system according to one of thepreviously described exemplary embodiments. The system is functionallyconnected to the internal combustion engine for use of the waste heat ofthe engine. The system can be used to convert the waste heat intomechanical and/or electrical energy, which is sent back to the internalcombustion engine again, such as to a crankshaft of the internalcombustion engine, especially by means of an electric motor, which isfunctionally connected to the crankshaft. Alternatively or in addition,the energy converted in the system from the waste heat of the internalcombustion engine can be sent to an external consumer or to a powersupply system. It is possible that the power supply system could be anon-board power supply system of a motor-driven vehicle which comprisesthe arrangement. The system makes it possible to achieve a considerableincrease in the efficiency of the internal combustion engine through theuse of its waste heat. Instead of being uselessly dissipated into theenvironment, the waste heat is put to positive use.

The internal combustion engine of the arrangement is preferablyconfigured as a reciprocating piston engine. In a preferred exemplaryembodiment, the internal combustion engine serves in particular to driveheavy land vehicles such as mining vehicles and trains or water craft,wherein the internal combustion engine is used in a locomotive or motorcoach or in a ship. The use of the internal combustion engine to drive avehicle serving defensive purposes such as a tank is also possible. Inanother exemplary embodiment of the internal combustion engine, it isstationary and used for stationary power generation to generateemergency power or to cover continuous-load or peak-load demands,wherein the internal combustion engine in this case preferably drives agenerator. The stationary use of the internal combustion engine to driveauxiliary units such as fire-fighting pumps on offshore drilling rigs isalso possible. An application of the internal combustion engine in thearea of the recovery of fossil materials and especially fossil fuelssuch as oil and/or gas is also possible. The internal combustion enginecan also be used in industry or in the construction field for theproduction of construction vehicles such as cranes and bulldozers. Theinternal combustion engine is preferably configured as a diesel engine;as a gasoline engine; or as a gas engine for operation with natural gas,biogas, customized gas, or some other suitable gas. Especially when theinternal combustion engine is configured as a gas engine, it is suitablefor use in block-type thermal power stations for stationary powergeneration.

The goal is also achieved by a motor vehicle that is characterized by anarrangement according to one of the previously described exemplaryembodiments. With respect to the motor-driven vehicle, the advantagesalready explained in conjunction with the cooling device, the system,and the arrangement are realized. The energy converted by the systemfrom the waste heat of the internal combustion engine can be usedeffectively either to support the internal combustion engine or forother purposes, such as to supply an on-board power supply system of themotor-driven vehicle with electrical energy.

In an exemplary embodiment the motor-driven vehicle is configured as awater craft, especially as a ship, preferably as a ferry. Here the wasteheat can be used in a variety of ways to operate various systems of theship, especially an on-board power supply system, i.e., the ship's ownpower grid, or to support the internal combustion engine. It inaddition, it is also possible to realize the recooling device in a watercraft in an especially simple and low-cost manner by using sea water orriver water for the recooling. Thus a virtually inexhaustible heatreservoir is available for recooling, so that, whatever else may happen,the precise setting of the thermodynamic state of the working medium inthe condenser cannot fail because of a lack of recooling capacity.

The goal is also achieved, finally, in that a method for operating athermodynamic cycle, quite preferably an organic Rankine cycle, iscreated. The method is provided in particular for the operation of asystem according to one of the previously described exemplaryembodiments. In this case the system comprises an evaporator, anexpansion device, and a condenser, arranged in that order in thedirection in which the working medium flows through the circuit of thesystem, wherein it also comprises a cooling device, preferably a coolingdevice according to one of the preceding exemplary embodiments. Withinthe scope of the method, the desired cooling capacity of the condenseris achieved by actuation of the variable-output conveying device of thecooling device and/or by actuation of a mixing device for supplying avariable portion of coolant from a hot branch of the cooling device to acold branch of the cooling device via a connecting line. The coolingcapacity of the condenser is preferably adjusted by appropriateactuation of both the conveying device and the mixing device. Thus theadvantages which have already been described in conjunction with thecooling device, the system, the arrangement, and the motor-drivenvehicle are realized.

Within the scope of the method, a pump, especially a variable-speedpump, is used as the conveying device, wherein the output of the pump isadjusted by varying its rotational speed.

In an embodiment of the method the output of the conveying device and/ora functional setting of the mixing device is automatically controlled.This makes possible an especially precise setting of the coolingcapacity of the cooling device and thus simultaneously of the coolingcapacity of the condenser. Preferably both the output of the conveyingdevice and the functional setting of the mixing device are automaticallycontrolled.

Finally, in another embodiment of the method the cooling capacity of thecooling device is automatically controlled to achieve the optimal poweryield of the system and/or a presettable absolute or relativetemperature level of the working medium in the condenser or immediatelydownstream from the condenser. Thus an optimal power yield can beguaranteed at all operating points of the system in an especiallysuitable and exact manner.

The description of the cooling device and of the system on the one handand of the method on the other hand are to be understood ascomplementary to each other. In particular, method steps which have beenexplained explicitly or implicitly in conjunction with the coolingdevice or the system are preferably steps, individually or incombination, of a preferred embodiment of the method. In the same way,features of the cooling device or of the system which have beenexplained explicitly or implicitly in conjunction with the method arepreferably features, individually or in combination, of a preferredexemplary embodiment of the cooling device or of the system. The coolingdevice or the system is preferably characterized by at least one featurewhich is required by at least one method step of the method. The methodis characterized preferably by at least one method step which isrequired by at least one feature of the cooling device or of the system.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of the disclosure. For a better understanding of the invention, itsoperating advantages, specific objects attained by its use, referenceshould be had to the drawings and descriptive matter in which there areillustrated and described preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWING

In the drawing:

FIG. 1 shows a schematic diagram of an exemplary embodiment of amotor-driven vehicle with an arrangement consisting of an internalcombustion engine and a system with a cooling device;

FIG. 2 shows a schematic diagram of an exemplary embodiment of thecooling device; and

FIG. 3 shows a schematic diagram of an embodiment of the method in theform of an automatic control circuit.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a schematic diagram of an exemplary embodiment of amotor-driven vehicle 1, which comprises an arrangement 3 consisting ofan internal combustion engine 5 and a system 7 for operating athermodynamic cycle, here in particular an organic Rankine cycle (ORC).The motor-driven vehicle 1 is preferably configured as a ship.Alternatively, however, an embodiment of the motor-driven vehicle 1 as arail vehicle, as a mining or construction vehicle, as a defensivevehicle, as a truck, or even as a passenger vehicle is also possible.

The use of the arrangement 3 is not limited to motor-driven vehicles;instead, it can be used in other areas as well, including stationaryuses of the internal combustion engine 5 to operate pumps on an offshoredrilling rig, for example, where the waste heat of the engine can be putto positive use.

Finally, the system 7 is not limited to use in an arrangement with aninternal combustion engine 5. On the contrary, it can be used in otherways to use waste heat such as to use industrial waste heat or even touse other heat sources such as geothermal heat.

The system 7 comprises a working medium circuit 9, along which anevaporator 11, an expansion device 13, and a condenser 15 are arrangedin that order in the flow direction of the working medium. The workingmedium is conveyable through the working medium circuit 9 by a workingmedium pump 17. The working medium used is preferably ethanol.

The expansion device 13 is preferably configured as a continuous-flowmachine or as a displacement machine, especially as a turbine, as areciprocating piston expander, as a rotary vane pump, as a Rootsexpander, or as a scroll expander. A configuration of the expansiondevice 13 as a helical screw expander, however, is especially preferred.The expansion device 13 is functionally connected to a generator 19 toconvert mechanical energy recovered in the expansion device 13 intoelectrical energy.

The evaporator 11 is functionally connected to the internal combustionengine 5 preferably in such a way that waste heat contained in theexhaust gas and/or in the coolant circuit of the internal combustionengine 5, in particular the waste heat contained in the exhaust gas ofthe engine, can be sent to the working medium of the system 7 in theevaporator 11.

To cool the working medium in the condenser 15, in particular tocondense it, a cooling device 21 is provided with a coolant circuit 23.A sensor device 25 for detecting a temperature and/or a pressure of theworking medium in the condenser 15 is provided preferably directlydownstream from the condenser 15 or even in the condenser 15. Theformulation “in the condenser” is always to be understood not only as avalue detected directly inside the condenser 15 but also as a valuedetected immediately downstream from it, because, if these values differat all from each other, the difference is irrelevant. The sensor device25 is functionally connected to a control unit 27, which for its ownpart is functionally connected to the cooling device 21 to adjust itscooling capacity.

It has been found that the waste heat supplied to the evaporator 11varies as a function of an operating point of the internal combustionengine 5. Thus an operating point of the system 7 varies at the sametime, as well as the cooling capacity of the cooling device 21 requiredto achieve an optimal power yield of the system. The cooling capacity isadjusted precisely by means of the cooling device 21 and the controlunit 27 to achieve the optimal power yield at every operating point ofthe system 7.

FIG. 2 shows a schematic diagram of an exemplary embodiment of thecooling device 21. Also shown are the condenser 15, a working mediumfeed line 29 to the condenser 15, and a working medium outlet line 31leading from the condenser 15. The broken line “L” marks the systemboundary between the condenser 15 and the rest of the system 7.

The cooling device 21 comprises the coolant circuit 23, which isconfigured as a primary coolant circuit. A conveying device 33, hereconfigured as a pump, is provided to convey coolant around the coolantcircuit 23, where the conveying device 33 comprises a variable output,here a variable rotational speed for producing the desired volume flowrate of coolant in the coolant circuit 23. The coolant circuit 23comprises a cold branch 35 located downstream—with respect to the flowdirection of the coolant—from a cooling point 37, which is configuredhere as a recooling device 39, and a hot branch 41, upstream of thecooling point 37. Between the hot branch 41 and the cold branch 35, aconnecting line 43 is arranged, and a mixing device 45 is provided,which is configured here as a three-way mixer 47, by means of which avariable portion of coolant from the hot branch 41 can be sent via theconnecting line 43 to the cold branch 35. The functional setting of themixing device 45 is variably adjustable, so that a variable mixing ratiobetween the hot coolant arriving through the connecting line 43 and thecold coolant arriving from the cooling point 37 can be set.

The cold branch 35 passes via a first connector 49 to a second connector51, wherein the connecting line 43 leads to a third connector 53 of thethree-way mixer 47.

The arrows P in FIG. 2 indicate the flow direction of the coolant in thecoolant circuit 23, wherein the coolant is conveyable by the conveyingdevice 33 around the coolant circuit 23 in the indicated flowdirections.

It is obvious here that the connecting line 43 branches off from the hotbranch 41 upstream of the recooling device 39, wherein it leads to thecold branch downstream from the recooling device 39, wherein it leads inparticular into the cold branch at a point upstream of the conveyingdevice 33.

The recooling device 39 is configured to recool the coolant by means ofa recooling medium, which is conveyable by a recooling medium pump 55around a recooling path 57, which is preferably configured as asecondary coolant circuit. Sea water is preferably used here as therecooling medium, especially in the case of an embodiment of themotor-driven vehicle 1 as a ship. If the ship is configured as a riverboat, however, preferably river water is used as the recooling medium.

In other applications of the system 7, it is possible to provide, as analternative, that air, especially ambient air, or a thermal connectionwith some other external heat reservoir is used as the recooling medium.Tap water, for example, is another possible example of a recoolingmedium.

The coolant circuit 23 also comprises a compensating reservoir 59 forthe coolant.

FIG. 2 shows the control unit 27, which is functionally connected to thesensor device 25 for detecting the thermodynamic state of the workingmedium in the condenser 15, especially for detecting the temperatureand/or the pressure of the working medium.

The control unit 27 is also functionally connected to the conveyingdevice 33 for open-loop or closed-loop control of its output, especiallyfor the open-loop or closed-loop control of the rotational speed of aconveying device 33 configured as a pump. In addition, the control unit27 is functionally connected to the mixing device 45 for the open-loopor closed-loop control of its functional setting. By means ofappropriate actuation of the mixing device 45, a temperature of thecoolant downstream from the mixing device 45 and thus in particular acoolant inlet temperature into the condenser 15 can be automaticallycontrolled, wherein at the same time, by application actuation of theconveying device 33, a volume flow rate of the coolant through thecoolant circuit 23 and especially through the condenser 15 can beautomatically controlled. Overall, therefore, the cooling capacity ofthe cooling device 21 is automatically controllable preferably as afunction of an operating point of the system 7. It is thus possible toadjust precisely the state of the working medium downstream from thecondenser 15. This is possible in particular because of the coolingdevice 21, even though the temperature of the recooling medium in therecooling path 57 typically cannot be controlled in open-loop orclosed-loop fashion and instead is determined by external circumstances.This is obvious when sea water or ambient air is used as the recoolingmedium.

Water is preferably used as the coolant in the cooling device 21 andespecially in the coolant circuit 23.

FIG. 3 shows a schematic diagram of an embodiment of the method in theform of an automatic control circuit. A setpoint 61 in the form of anominal value of a thermodynamic variable of state of the working mediumin the condenser 15, preferably a nominal temperature or a nominalsupercooling of the working medium is entered into the automatic controlcircuit. An actual value 63 of the thermodynamic state variable, whichis preferably measured by the sensor device 25, is sent back to acomparison member 65, and a control deviation 67 between the setpoint 61and the actual value 63 is determined.

The setpoint 61 is preferably taken from a characteristic diagram, whichis based on at least one operating parameter of the system 7 forcharacterizing its operating states. As an alternative, it is alsopossible to select a constant setpoint 61 for the operation of thesystem 7. In this case, the cooling capacity of the cooling device 21 isarrived at in particular as a function of the heat input into thevaporizer 11.

The control deviation 67 is sent to the controller 69, which, on thisbasis, calculates two values for the actuators, namely, a first startingvalue 71 for the output of the conveying device 33, especially arotational speed of the conveying device 33 configured as a pump, and asecond starting value 73 for the actuation of the mixing device 45. Thetwo starting values 71, 73 act on a controlled system 75 comprising inparticular the mixing device 45 and the conveying device 33 as well as,finally, the condenser 15. The output of the conveying device 33 and thefunctional setting of the mixing device 45 are preferably adjusted tomatch the default values 71, 73, which is not shown here explicitly. Tothis extent, what is involved is subsidiary automatic control.

In the controlled system 75, a new actual value 63 for the thermodynamicstate variable of the working medium in the condenser 15 is thenreached.

Quite generally, within the scope of the method, therefore, the coolingcapacity of the condenser 15 of the system 7 is adjusted by actuation ofthe variable-output conveying device 33, wherein in addition the mixingdevice 45 is actuated to supply a variable portion of coolant from thehot branch 41 to the cold branch 35 via the connecting line 43.

If a constant value is selected for the setpoint 61, this value ispreferably determined in such a way that the system 7 delivers thegreatest possible power yield at all operating points. If the setpoint61 is taken from a characteristic diagram, this preferably shows thevalues for the desired setpoint 61 at which the system 7 supplies itsoptimal power yield as a function of its operating point. Accordingly,the cooling capacity of the cooling device 21 is automaticallycontrolled especially to result in the optimal power yield of thesystem. 7.

Overall it has been found that, by means of the method, it is possibleautomatically to control the cooling capacity of the cooling device 21in an energy-saving and yet very precise manner, so that the system 7can operate with its optimal power yield.

While specific embodiments of the invention have been shown anddescribed in detail to illustrate the inventive principles, it will beunderstood that the invention may be embodied otherwise withoutdeparting from such principles.

We claim:
 1. A cooling device for a condenser of a system for athermodynamic cycle, comprising: a coolant circuit; a conveying devicefor conveying a coolant through the coolant circuit, wherein the coolantcircuit comprises a cold branch downstream from a cooling point for thecoolant and a hot branch upstream of the cooling point, wherein theconveying device has a variable output, and/or the coolant circuitcomprises a connecting line between the hot branch and the cold branch;and a mixing device provided so that a variable portion of coolant fromthe hot branch is sendable to the cold branch via the connecting line,bypassing the cooling point.
 2. The cooling device according to claim 1,wherein the conveying device is configured as an automaticallycontrollable conveying device.
 3. The cooling device according to claim1, and further comprising a recooling device set up to cool the coolantin the coolant circuit, wherein the connecting line branches off fromthe hot branch upstream of the recooling device, wherein the connectingline leads to the cold branch downstream from the recooling device. 4.The cooling device according to claim 1, wherein the connecting lineleads to the cold branch upstream of the conveying device.
 5. Thecooling device according to claim 1, wherein the mixing device is athree-way mixer, wherein the cold branch passes through a first and asecond connector of the three-way mixer, and wherein the connecting lineleads to a third connector of the three-way mixer.
 6. The cooling deviceaccording to claim 1, further comprising a control unit operative toproduce a presettable absolute or relative temperature level in thecondenser of the system for a thermodynamic cycle by actuation of theconveying device and/or of the mixing device.
 7. The cooling deviceaccording to claim 6, wherein the control unit is operative to optimizea power yield of the system for a thermodynamic cycle by actuation ofthe conveying device and/or by actuation of the mixing device.
 8. Asystem for a thermodynamic cycle, comprising a cooling device accordingto claim
 1. 9. The system according to claim 8, wherein the system isconfigured to use waste heat of an internal combustion engine.
 10. Anarrangement, comprising: an internal combustion engine; and the systemaccording to claim
 8. 11. A motor-driven vehicle comprising thearrangement according to claim
 10. 12. The motor-driven vehicleaccording to claim 11, wherein the motor-driven vehicle is a watercraft.
 13. The motor-driven vehicle according to claim 12, wherein thewater craft is a ship.
 14. A method for carrying out a thermodynamiccycle, for operating a system having an evaporator, an expansion device,a condenser, and a cooling device according to claim 1, the methodcomprising the step of adjusting cooling capacity of the condenser byactuation of a variable-output conveying device of the cooling deviceand/or by actuation of a mixing device for supplying a variable portionof coolant from a hot branch of the cooling device to a cold branch ofthe cooling device via a connecting line.
 15. The method according toclaim 14, including controlling an output of the conveying device and/ora functional setting of the mixing device.
 16. The method according toclaim 14, including controlling cooling capacity to provide an optimalpower yield of the system or to produce a presettable absolute orrelative temperature level in the condenser.